This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7 119 from an application for TENSION MASK FOR FLAT CATHODE RAY TUBE earlier filed in the Korean Industrial Property Office on Dec. 4, 2000, and there duly assigned Serial No. 2000-72936 by that Office.
1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a tension mask assembly having a slot of an improved structure, in which a dummy bridge is formed, and having a color selecting function for a flat cathode ray tube.
2. Description of the Related Art
Generally, a flat cathode ray tube includes a panel having a flat screen and a funnel having is an electronic gun at a neck portion and a deflection yoke at a cone portion. Such a cathode ray tube employs a tension mask for accurately landing red, green and blue electron beams emitted from the electron gun on the phosphor screen. The tension mask is disposed to be a predetermined gap apart from a phosphor screen formed on the inner surface of the panel.
An exemplar of the art U.S. Pat. No. 4,926,089 issued to Moore for Tied Slit Foil Shadow Mask with False Ties discloses a tension mask.
The tension mask includes a plurality of strips which is formed on a metal foil such that they are separated from one another at predetermined intervals, slots intermittently formed between the strips for allowing many electron beams to pass, real bridges for supporting the slots, and dummy bridges extending from the strips to the slots. At least one dummy bridge is formed for each slot.
A plurality of dummy bridges extending from opposite strips toward the center of the slot are formed along the opposite borders of the slot. The dummy bridges face the center of the slot at the strip so that they are located on opposed sides of the slot. Accordingly, a width of the slot in which dummy bridges are not formed is different from a width of the slot at which the dummy bridges are formed.
A tension mask having such a structure is formed by an etching method. An etching process is performed so that a clipping phenomenon, in which an electron beam emitted from an electron gun can be blocked by the tension mask, is suppressed at a portion of the slot in which the dummy bridge is not formed. In other words, to prevent an electron beam from colliding with the strip, an etching process is performed such that a lower end surface of a first strip is less etched than an upper end surface thereof in a direction in which an electron beam is deflected and a lower end surface of a second strip is less etched than the lower end surface of the first strip. Accordingly, an electron beam can pass through the slot without being clipped.
For a portion of the slot in which the dummy bridge is formed, a lower end surface of a first dummy bridge is more etched than an upper end surface thereof and an upper end surface of a second dummy bridge is more etched than a lower end surface thereof. As a result, although the width of the portion of the slot in which the dummy bridges are formed is narrower than the width of the portion of the slot in which the dummy bridges are not formed, a deflected electron beam can pass through the portion of the slot having the dummy bridges.
A conventional tension mask has the following problems. During a procedure in which electron beams emitted from an electron gun pass through slots and then land on the phosphor screen of a panel so as to display an image on a screen, passing of electron beams occurs at portions where dummy bridges are formed so that traces appearing due to real bridges and dummy bridges which shade the phosphor screen cannot be uniform. Consequently, the problem of visibility cannot be overcome completely. Therefore, it is desired to change the shape of a slot at which a dummy bridge is formed in order to solve the problem of visibility.
In addition, in order to adjust the degree of a shadow occurring when a deflected electron beam passes through the portion of each slot having dummy bridges, it needs to form a long dummy bridge. Accordingly, a design margin of a dummy bridge is deficient.
It is therefore an object of the present invention to provide a tension mask assembly for a flat cathode ray tube, in which the structure of a dummy bridge formed at a slot is improved to completely solve a visible line problem so that the definition of an image can be improved.
It is another object to provide a tension mask assembly that is easy to manufacture.
It is another object to have a tension mask that is inexpensive to manufacture.
It is yet another object to have a tension mask that can accommodate the manufacture of a high definition cathode ray tube.
Accordingly, to achieve the above object of the invention, there is provided a tension mask assembly for a flat cathode ray tube. The tension mask assembly includes a tension mask having a plurality of strips separated from one another by a predetermined gap, real bridges connecting adjacent strips to thus define slots through which electron beams pass, and first and second dummy bridges extending from adjacent strips toward each slot therebetween, the tension mask being installed such that its top surface faces a panel forming a screen and it is separated from the panel by a predetermined gap, a plurality of supporting members disposed at opposite sides of the tension mask to support the tension mask, and a plurality of rigid members secured to opposite ends of the supporting members to apply tension to the tension mask. A first etching boundary formed at an end of the first dummy bridge near to the center of the tension mask is lower with respect to the screen than a second etching boundary formed at an end of the second dummy bridge near to the periphery of the tension mask.
In addition, the vertical center axis of an etched area at the upper end surfaces of the first and second dummy bridges is offset from the vertical center axis of an etched area at the lower end surfaces of the first and second dummy bridges toward the center of the tension mask so that a deflected electron beam can be blocked. The amount of offset increases from the center of the tension mask toward the periphery thereof.
Moreover, an etched area at the upper end surfaces of the first and second dummy bridges is wider than an etched area at the lower end surfaces of the first and second dummy bridges.
Furthermore, an etched area at an upper surface above the first etching boundary of the first dummy bridge is wider than an etched area at a lower surface therebelow, and an etched area at a lower surface below the second etching boundary of the second dummy bridge is wider than an etched area at an upper surface thereabove.